In this chapter, you learned about the components of an RFID interrogator, which include the oscillator, transmitter, receiver, communication and antenna interfaces, and a control unit carrying the controller and processor, as well as memory.
Next, you discovered the interrogator's functions. You learned that interrogators are capable of reading tags and writing to the tags, that the read range can be longer than the write range, and that the reading operation takes less time than the writing operation.
Interrogators can directly manage various I/O devices such as light stacks or audible devices and offer a GUI for easy configuration. You saw how to access the GUI to communicate with the reader and discovered which settings can be configured through this interface.
I discussed how interrogators can be updated through firmware upgrades. It is appropriate to upload a new firmware version only when it fixes existing problems that were giving you a hard time or when it provides additional capabilities to the interrogator such as supporting new tag types or ensuring compatibility with new protocols (such as Generation 2, for instance).
You discovered the differences between a "dumb" reader and a "smart" reader as well as the capabilities the smart reader can provide. The smart readers can not only manage I/O, but also provide processing and filtering capabilities, data aggregation and transfer in real time or in batches, operation in dense reader mode, and assistance with anticollision.
You also learned about various communication methods between readers and tags including inductive coupling and passive backscatter, as well as about restrictions imposed on the radiated power that vary by region. The United States allows up to 4 watts of EIRP when hopping minimally across 50 channels in a band 26 MHz wide, whereas Europe allows up to 2 watts of ERP (which equals about 3.6 W EIRP) in a band 2 MHz wide while employing listen-before-talk.
In the tag population management section, you learned that interrogators use a set of commands including the Select command, which is used to pick out a group of tags based on a part of their EPC number; the Inventory command, which is used to singulate one tag from the group created by the Select command; and the Access command, which is used for accessing the tag and performing various data operations. Some of the subcommands of the Access command are Kill, Lock, Read, and Write.
You also learned about types of interrogators. Fixed interrogators are usually attached to an RFID portal or tunnel and usually use cables for their power as well as communication. I also discussed various kinds of mobile interrogators: vehicle-mounted interrogators are usually ruggedized and differently shaped versions of the fixed units implemented with forklifts or clamp trucks, and handhelds are portable because of their small size, integrated antenna, and wireless communication. There are other kinds of mobile devices, such as readers integrated into cell phones, PCMCIA cards, or reader modules used by OEM manufacturers.
After the interrogator construction, functions, and types, I described the factors that affect the performance of an interrogation zone. You learned that an appropriate dwell time is necessary to achieve successful reading of and/or writing to a tag.
Then I discussed the aspects of antenna performance, including types of antenna polarization, such as linear or circular polarization, and identified the differences between bi-static and mono-static antennas. Linear antennas produce more-coherent waves without phase distortion; therefore, they are a bit more efficient than circular antennas. However, they are more orientation sensitive. Circular antennas, on the other hand, are not orientation sensitive, but because of propagating in a circular manner and because of phase distortion, they are slightly less effective. In addition, bi-static antennas have two antennas with dedicated transmitting and receiving functions, whereas mono-static antennas switch these functions by using a circulator.
Next, you learned that the antenna field has imperfections, and that antenna coverage increases with increased power input. This was followed by a discussion about antenna configurations in the form of RFID portals and tunnels as well as their function, suitable use, and customization according to your environment and application. You also got some ideas about antenna tuning, and that to achieve proper shielding you should use absorptive materials such as metal mesh or anechoic foam instead of reflective materials that could cause reflections and interference.
The following section discussed the characteristics and challenges of the dense reader environment. You found out that you could overcome these challenges by using synchronization methods such as time-division or frequency-division multiplexing, the listen-before-talk technique, and frequency hopping.
You also learned that if two or more tags respond at the same time, the reader cannot communicate with either of them and, therefore, anticollision algorithms must be put in place. You have a choice between probabilistic and deterministic algorithms. Probabilistic algorithms use a slotted ALOHA protocol and its variation is used by Generation 2 tags. Deterministic algorithms use a binary-tree, or tree-walking, scheme.
In sum, you learned all the basics you need to know to understand the characteristics and functions of an interrogation zone. Your knowledge will be supplemented by the chapters that follow this one discussing system design, installation, and troubleshooting, as well as everything you need to know about RFID tags. Although this chapter touched on various regulations, they will be discussed in detail in Chapter 9, "Standards and Regulations."